Frequency references provided by oscillators are required in every clocked electronic system, including communication circuits, microprocessors, and signal processing circuits. The operating frequency typically used in time control applications is 32.768 kHz. Oscillators frequently consist of high performance piezoelectric crystals, such as quartz oscillators. The advantages of quartz oscillators are their stable operating frequency and high quality factor. However, the disadvantages of quartz oscillators are their relatively large size and unsuitability for high integration with electronic circuitry (e.g., CMOS circuits).
Based on these limitations of conventional oscillators, there is a strong interest in the development of fully integrated silicon oscillators. Integration is important not only for reduced size but also reduced power consumption. It is possible to realize an integrated silicon oscillator using the mechanical properties of silicon devices. For example, silicon microelectromechanical (MEMs) resonators can provide small form factor, ease of integration with conventional semiconductor fabrication techniques and high f.Q products. Accordingly, MEMs resonators are considered a desirable alternative to quartz resonators in real-time clock applications. One example of a silicon-based MEMs resonator that may be used for real-time clock applications is disclosed in an article by A. Pomarico et al., entitled “Vertical MEMS Resonators for Real-Time Clock Applications,” Journal of Sensors, Vol. 2010, Article ID 362439.